Sheet to Form a Protective Shield for Chips

ABSTRACT

A sheet to form a protective film for chips includes a release sheet and a protective film forming layer formed on a detachable surface of the release sheet. The protective film forming layer includes a thermosetting and/or energy ray-curable component and a binder polymer component.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.11/113,480 filed Apr. 25, 2005, which is itself a division of U.S.patent application Ser. No. 10/102,583 filed Mar. 20, 2002, now U.S.Pat. No. 6,919,262, and also relates to U.S. patent application Ser. No.11/113,481 filed Apr. 25, 2005, now U.S. Pat. No. 7,235,465, all ofwhich are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet to form a protective film forchips, which enables to efficiently form a protective film on a backsurface of a semiconductor chip, and thereby contributes to improvementin production efficiency of chips. More particularly, the presentinvention relates to a sheet to form a protective film for chips, whichis used in production of semiconductor chips by face down mountingprocess.

The present invention also relates to a process for producingsemiconductor chips, using the sheet to form a protective film forchips.

2. Description of the Prior Art

Recently, production of semiconductor devices is made through aso-called face down mounting process. In the face down process, chipsare electrically connected with a substrate through a convex portion(bump) formed on a circuit surface of the chip to ensure itsconductivity to the substrate.

Semiconductor devices are generally produced through the followingsteps:

(1) forming a circuit on a surface of a semiconductor wafer by etchingor the like and providing a bump on the appointed position of thecircuit surface;

(2) grinding a back surface of the semiconductor wafer to have a giventhickness;

(3) fixing the back surface of the semiconductor wafer onto a dicingsheet which is tautly supported by a ring frame, and dicing the wafer toseparate each circuit by the use of a dicing saw to obtain semiconductorchips; and

(4) picking up the semiconductor chips to mount them face down on aprescribed substrate and sealing the chip in a resin or coating the backsurface of the chip with a resin according to necessity for chipprotection, thereby obtaining a semiconductor device.

The resin sealing is performed by dripping resin in a proper amount onthe chip (potting method) or using a mold (molding method), bothfollowed by curing. The potting method has a drawback of difficulty indripping a proper amount of resin. The molding method involves washingof the mold, which will require additional costs for equipment andoperation thereof.

The resin coating may cause ununiform quality because of the difficultyin spreading a proper amount of resin evenly on the chips.

Therefore, the technique which is capable of forming a highly uniformprotective film on a back surface of the chip by simplified operationhas been desired.

In the grinding of the back surface of the wafer in step (2), minutestreaky scratches are formed on the back surface of the chip owing tothe use of a grinding machine. The minute scratches may cause cracksduring the dicing in step (3) or after the device is packaged. As such,it has been conventionally required in some cases to perform chemicaletching after the mechanical grinding to eliminate the minute scratches.The chemical etching, as a matter of course, raises problems related tothe cost increase for its equipment and operation.

Therefore, the technique for prevailing adverse effects resulting fromminute scratches has been desired, even if minute scratches are left onthe back surface of the wafer as a result of mechanical grinding.

In light of the above prior art, it is an object of the presentinvention to provide a process through which a highly uniform protectivefilm can be readily formed on a back surface of the chip, and, even ifminute scratches are formed on the back surface of the chip as a resultof mechanical grinding, the chip is prevailed over adverse effectsresulting from the scratches. It is another object of the invention toprovide a sheet to form a protective film for chips employable in theabove process.

SUMMARY OF THE INVENTION

A first sheet to form a protective film for chips according to thepresent invention comprises a release sheet and a protective filmforming layer formed on a detachable surface of the release sheet,wherein said protective film forming layer comprises a thermosetting orenergy ray-curable component and a binder polymer component.

A second sheet to form a protective film for chips according to thepresent invention comprises a release sheet and a protective filmforming layer formed on a detachable surface of the release sheet,wherein said protective film forming layer comprises a thermosettingcomponent, an energy ray-curable component and a binder polymercomponent.

In the invention, the binder polymer component, the thermosettingcomponent and the energy ray-curable component are preferably composedof an acrylic polymer, an epoxy resin and an ultraviolet ray-curableresin, respectively.

When the sheet to form a protective film for chips is employed in theprocess of the invention (mentioned later), a highly uniform protectivefilm can be readily formed on a back surface of the chip and, even ifminute scratches are formed on the back surface of the chip as a resultof mechanical grinding, the chip is prevailed over adverse effectsresulting from the scratches.

The first process for producing semiconductor chips having a protectivefilm on the back surface comprises:

adhering a protective film forming layer of the first or second sheet toform a protective film for chips according to the present invention ontoa back surface of a semiconductor wafer having circuits on its surface,and thereafter, further conducting the following steps 1 to 3 in anarbitrary order:

Step 1: detaching the release sheet from the protective film forminglayer;

Step 2: curing the protective film forming layer by heating or energyray irradiation;

Step 3: dicing the semiconductor wafer together with the protective filmforming layer with respect to each circuit.

The second process for producing semiconductor chips having a protectivefilm on the back surface comprises:

adhering a protective film forming layer of the second sheet to form aprotective film for chips according to the present invention onto a backsurface of a semiconductor wafer having circuits on its surface,

curing the protective film forming layer by irradiation with energy ray,and thereafter, further conducting the following steps 1 to 3 in anarbitrary order:

Step 1: detaching the release sheet from the protective film forminglayer;

Step 2: further curing the protective film forming layer by heating;

Step 3: dicing the semiconductor wafer together with the protective filmforming layer with respect to each circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of the sheet to form a protective film forchips of the present invention;

FIGS. 2 to 7 are flow sheets of processes for producing semiconductorchips of the present invention;

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in detail with reference to thedrawings.

The first sheet 10 to form a protective film for chips of the inventioncomprises, as shown in FIG. 1, the release sheet 1 and the protectivefilm forming layer 2 formed on a detachable surface of the release sheet1.

The release sheet 1 can be composed of a film of, e.g., polyethylene,polypropylene, polybutene, polybutadiene, polymethylpentene, polyvinylchloride, vinyl chloride copolymer, polyethylene terephthalate,polyethylene naphthalate, polybutylene terephthalate, polyurethane,ethylene-vinyl acetate, ionomer-resin, ethylene/(meth)acrylic acidcopolymer, ethylene/(meth)acrylate copolymer, polystyrene,polycarbonate, polyimide, and fluorine resin. A film of a crosslinkedproduct of the above polymers, or a laminated film of the above filmscan be used as well.

When the release sheet is detached after the curing of the protectivefilm forming layer, films of polymethylpentene, polyethylene naphthalateand polyimide are particularly preferable for their excellent heatresistance.

The release sheet 1 has a surface tension of 40 mN/m or less, preferably37 mN/m or less, highly preferably 35 mN/m or less. The low surfacetension of the release sheet 1 can be attained by appropriatelyselecting the sheet material or coating a silicone resin on the surfaceof sheet 1 for release treatment.

The release sheet 1 has a thickness of generally 5 to 300 μm, preferably10 to 200 μm, particularly preferably 20 to 150 μm.

The protective film forming layer 2 of the first sheet to form aprotective film for chips is composed of a thermosetting or energyray-curable component and a binder polymer component.

The protective film forming layer 2 of the second sheet to form aprotective film for chips is composed of a thermosetting component, anenergy ray-curable component and a binder polymer component.

Examples of the thermosetting component include epoxy resin, phenolresin, melamine resin, urea resin, polyester resin, urethane resin,acrylic resin, polyimide resin, benzoxazine resin and mixtures thereof.In the invention, epoxy resin, phenol resin and a mixture thereof arepreferably employed.

The epoxy resin can make a rigid coat with three dimensional networkwhen heated. Various known epoxy resins have been conventionally used.Preferably, the epoxy resin has a molecular weight of around 300 to2000. Particularly preferred is a blend of epoxy resins containing aliquid one in an ordinary state, having a molecular weight of 300 to500, preferably 330 to 400 and the solid one at ordinary temperature,having a molecular weight of 400 to 2500, preferably 500 to 2000. Theepoxy resin preferably used in the invention has an epoxy equivalent of50 to 5000 g/eq. Examples for such epoxy resin include glycidyl ethersof phenol, e.g., bisphenol A, bisphenol F, resorcinol, phenol novolakand cresol novolak; glycidyl ethers of alcohol, e.g., butanediol,polyethylene glycol and polypropylene glycol; glycidyl ethers ofcarboxylic acid, e.g., phthalic acid, isophthalic acid andtetrahydrophthalic acid; epoxy resins of the glycidyl- or alkylglycidyl-type, e.g., those of aniline isocyanurate in which activehydrogen bonded to nitrogen is substituted with a glycidyl group; andso-called alicyclic epoxides in which epoxy is introduced by oxidationof C—C double bond in the molecule, e.g., vinylcyclohexane diepoxide,3,4-epoxycyclohexylmethyl-e,4-dicyclohexane carboxylate and2-(3,4-epoxy)cyclohexyl-5,5-spiro(3,4-epoxy)cyclohenane-m-dioxane. Epoxyresins having a biphenyl, dicyclohexadiene or naphthalene skeleton canbe also employed.

Of these, epoxy resins of bisphenol-based glycidyl type, o-cresolnovolak type or phenol novolak type are preferable for the invention.These epoxy resins are used either individually or in combination.

The epoxy resin, when employed, is used together with an assistantadditive, i.e., a heat-activatable latent epoxy resin curing agent,preferably.

The heat-activatable latent epoxy resin curing agent does not react withan epoxy resin at room temperature but does react when activated underheating over a specific temperature.

To activate the heat-activatable latent epoxy resin curing agent, usecan be made of a method in which active species (anions, cations) aregenerated through the chemical reaction by heating, a method in whichthe agent, which has been stably dispersed in the epoxy resin at aroundroom temperature, is incorporated with the resin to dissolve therein athigh temperatures to initiate the curing reaction, a method in which thecuring agent encapsulated in a molecular sieve is eluted at hightemperatures to initiate the curing reaction, and a method using amicro-capsule.

Examples of the heat-activatable latent epoxy resin curing agent for usein the invention include various onium salts and active hydrogencompounds of high melting point, e.g., dibasic acid dihydrazidecompound, dicyandiamide, amine adduct curing agent and imidazolecompound.

These heat-activatable latent epoxy resin curing agents can be usedeither individually or in combination. The heat-activatable latent epoxyresin curing agent is used at 0.1 to 20 parts, preferably 0.2 to 10parts, highly preferably 0.3 to 5 parts by weight per 100 parts byweight of the epoxy resin.

Condensation products of aldehydes and phenols, e.g., alkylphenol,polyphenol and naphthol, can be used as the phenol resin withoutlimitations. Examples of the phenol resin preferably us3ed in theinvention include phenol novolak, o-cresol novolak, p-cresol novolak,t-butyl phenol novolak, dicyclopentadiene cresol, poly paravinyl phenoland bisphenol A novolak resins, and modified resins thereof.

The phenolic hydroxyl group contained in the phenol resin can readilyoccur addition reaction with an epoxy group in the epoxy resin whenheated to form a cured product high in impact resistance. Accordingly,the epoxy resin and the phenol resin can be used together.

The energy ray-curable component is composed of a compoundpolymerizable/curable by irradiation of an energy ray, e.g., ultravioletray and electron ray. The compound has at least one polymerizable doublebond in the molecule, and generally has a molecular weight of around 100to 30000, preferably around 300 to 10000. Exemplary compoundspolymerizable by energy ray irradiation include low molecular weightcompounds disclosed in Japanese Patent Laid-Open Publication Nos.60(1985)/196956 and 60(1985)/223139. Specifically, examples includetrimethylolpropane triacrylate, tetramethylolmethane tetraacrylate,pentaerythritol triacrylate, dipentaerythritol monohydroxypentaacrylate,dipentaerythritol hexaacrylate, 1,4-butyleneglycoldiacrylate,1,6-hexanedioldiacrylate, polyethyleneglycoldiacrylate,oligoesteracrylate, a urethaneacrylate oligomer of polyester orpolyether type, polyesteracrylate, polyetheracrylate, and epoxy-modifiedacrylate.

Of these, preferable for the present invention are ultravioletray-curable resins, specifically oligoesteracrylate and aurethaneacrylate oligomer.

Incorporation of a photopolymerization initiator in the energyray-curable component can shorten the polymerization/curing time andreduce the ray irradiation dose.

Examples of the photopolymerization initiator include benzophenone,acetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether,benzoin isopropyl ether, benzoin isobutyl ether, benzoin benzoic acid,benzoin methyl benzoate, benzoin dimethyl ketal,2,4-diethylthioxanthone, α-hydroxycyclohexylphenylketone,benzyldiphenylsulfide, tetramethylthiurammonosulfide,azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, andβ-chloroanthraquinone.

The photopolymerization initiator is suitably used at 1.5 to 4.5 partsby weight, preferably 2.4 to 3.8 parts by weight per 100 parts by weightof the energy ray-curable component.

The binder polymer component is employed for the purposes of impartingproper tackiness to the protective film forming layer 2 and improvingoperability of the sheet.

The binder polymer has a weight-average molecular weight of 50,000 to2,000,000, preferably 100,000 to 1,500,000, particularly preferably200,000 to 1,000,000. The sheet might not be formed adequately when themolecular weight of the binder polymer is too low, and not uniformlywhen too high because of poor mutual solubility of the polymer withother components.

Usable binder polymers are, for example, acrylic polymers, polyesterresin, urethane resin, silicone resin and rubber polymers. Acrylicpolymers are preferable.

Examples of the acrylic polymers include (meth)acrylate copolymerscomprising constituent units derived from a (meth)acrylate monomer andthose derived from a (meth)acrylic acid derivative. Preferably, the(meth)acrylate monomer is C₁₋₁₈ alkyl (meth)acrylate, e.g., methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate and butyl(meth)acrylate. Exemplary (meth)acrylic acid derivatives are(meth)acrylic acid, glycidyl (meth)acrylate and hydroxyethyl(meth)acrylate.

A glycidyl group may be introduced into the acrylic polymer chain bycopolymerization of glycidyl (meth)acrylate, thereby improving mutualsolubility of the polymer with an epoxy resin working as a thermosettingadhesive component (mentioned later). The copolymerization alsoincreases Tg of the cured product, thereby improving the heatresistance. Introducing a hydroxyl group into the acrylic polymer using,for example, hydroxyethyl acrylate facilitates controlling the adhesiontoward a chip and adhesion characteristics of the polymer.

The acrylic polymer has a weight average molecular weight of preferably100,000 or more, more preferably 150,000 to 1,000,000. The glasstransition temperature thereof is usually 20° C. or below, preferablyaround −70 to 0° C. The polymer has tackiness at ordinary temperature(23° C.).

Referring to the first sheet to form a protective film for chips, whenthe thermosetting component alone is incorporated in the protective filmforming layer 2, it is incorporated at usually 100 to 1500 parts,preferably 150 to 1000 parts, more preferably 200 to 800 parts by weightper 100 parts by weight of the binder polymer component. When the energyray-curable component alone is incorporated in the protective filmforming layer 2, it is incorporated at 5 to 500 parts, preferably 10 to200 parts, more preferably 20 to 150 parts by weight per 100 parts byweight of the binder polymer component.

Referring to the second sheet to form a protective film for chips, thethermosetting component and the energy ray-curable component areincorporated in the protective film forming layer 2 at 100 to 1500parts, preferably 150 to 1000 parts, more preferably 200 to 800 parts byweight in total per 100 parts by weight of the binder polymer component.At the same time, the weight ratio of the thermosetting component to theenergy ray-curable component (thermosetting component/energy ray-curablecomponent) is preferably 55/45 to 97/3, more preferably 60/40 to 95/5,particularly preferably 70/30 to 90/10.

Incorporation of the thermosetting component and the energy ray-curablecomponent with the binder polymer component in the above weight ratiogives a protective film which has proper tackiness before curing toallow secure application and exhibits excellent film hardness aftercuring.

The protective film forming layer 2 can be colored. Coloration for theprotective film forming layer 2 can be made by incorporating a pigmentor a dye therein. The colored protective film forming layer 2 improvesappearance of the resulting chips.

The protective film forming layer 2 may contain various additives inaddition to the above components. For example, electrically conductivefillers, e.g., gold, silver, copper, nickel, aluminum, stainless steel,carbon, ceramic, silver-coated nickel and silver-coated aluminum areadded for the purpose of imparting electrical conductivity after diebonding. Thermal conductive substances, such as metallic materials,e.g., gold, silver, copper, nickel, aluminum, stainless steel, siliconand germanium, and alloys thereof, are added for the purpose ofimparting thermal conductivity.

A coupling agent may be added in the protective film forming layer 2 toimprove adhesive properties and adhesion between the back surface of thechip and the cured protective film. The coupling agent improves adhesiveproperties, adhesion and water resistance (moist heat resistance) of theprotective film without deteriorating its heat resistance.

A preferable coupling agent is of silane type (silane coupling agent) inview of versatility and costwise merits.

The protective film forming layer 2 may contain a crosslinking agent,e.g., organic polyvalent isocyanate compound, organic polyvalent iminecompound and organometallic chelate compound, to adjust its initialadhesive and cohesive forces before cure.

An antistatic agent may be incorporated in the protective film forminglayer 2. Incorporation thereof inhibits static electricity occurrence toimprove the chip reliability.

A phosphoric acid, bromo or phosphorus compound can be incorporated inthe protective film forming layer 2 to impart flame resistance. Such afilm has improved reliability as a manufactured IC package.

The sheet 10 to form a protective film for chips is produced by coatingthe composition comprising the above components directly on a detachablesurface of the release sheet 1 using a conventional coater, e.g., a rollknife coater, a gravure coater, a die coater and a reverse coater, or bytransferring said composition on a detachable surface of the releasesheet 1, and drying the composition to form the protective film forminglayer 2. The composition can be coated on the detachable surface of therelease sheet in a state dissolved or dispersed in a solvent accordingto necessity.

The protective film forming layer 2 thus formed has a thickness ofusually 3 to 100 μm, preferably 10 to 60 μm.

The second sheet to form a protective film for chips of the presentinvention has common features, preferable embodiments inclusive, withthe first sheet to form a protective film for chips, except that theformer sheet has the protective film forming layer composed essentiallyof both thermosetting and energy ray-curable components.

The first or second sheet 10 to form a protective film for chips, whenemployed in the process for producing semiconductor devices (mentionedlater), can readily make a highly uniform protective film on a backsurface of a chip. Moreover, even if minute scratches are formed on theback surface of the chip as a result of mechanical grinding, the chip isprevailed over adverse effects resulting from the scratches.

The first process for producing semiconductor chips of the presentinvention will beg described with reference to the drawings.

The first process for producing semiconductor chips having a protectivefilm on the back surface comprises:

adhering a protective film forming layer of the first or second sheet toform a protective film for chips according to the present invention ontoa back surface of a semiconductor wafer having circuits on its surface,and thereafter, further conducting the following steps 1 to 3 in anarbitrary order:

Step 1: detaching the release sheet from the protective film forminglayer;

Step 2: curing the protective film forming layer by heating or energyray irradiation;

Step 3: dicing the semiconductor wafer together with the protective filmforming layer with respect to each circuit.

The process wherein the steps 1, 2 and 3 are conducted in this order(hereinafter, referred to as 1-2-3 mode production process) is firstdescribed with reference to FIG. 2.

The protective film forming layer 2 of the sheet 10 to form a protectivefilm for chips is applied onto a back surface of the semiconductor wafer3 having circuits on its surface (FIG. 2-A).

The release sheet 1 IS DETACHED FROM THE PROTECTIVE FILM FORMING LAYER2, AS SHOWN IN FIG. 2-B, to obtain a laminate composed of thesemiconductor wafer 3 and the protective film forming layer 2.

Then, the protective film forming layer 2 is cured by heating or energyray irradiation to form a protective film covering all the back surfaceof the wafer. FIG. 2-C illustrates the feature wherein the protectivefilm forming layer 2 is heated using a heating apparatus. The wafer withthe protective film has higher strength compared with the naked one,thereby decreasing breakage of the wafer during operation. Even ifminute scratches are formed on the back surface of the wafer as a resultof grinding, the protective film fills in the scratches, therebyprevailing the wafer over adverse effects resulting from the scratches.

The protective film of the invention is excellent in thicknessuniformity and the yield of its materials in comparison with protectivefilms produced by spreading a coating liquid directly on a back surfaceof the wafer or chip to make a protective film.

Next, as shown in FIG. 2-D, the laminate composed of the semiconductorwafer 3 and the protective film 2 is diced with respect to each circuitformed on the wafer surface. The dicing is performed so as to cut bothof the wafer and the protective film. The wafer dicing is performed bythe conventional method using a dicing sheet. As a result, semiconductorchips having a protective film on its back surface are obtained.

Finally, diced chips are picked up by the use of general means, e.g.,collets, thereby semiconductor chips having a protective film on itsback surface are obtained (FIG. 2-E).

According to the invention, a highly uniform protective film can bereadily formed on a back surface of a chip, and even if minute scratchesare formed on the back surface of the chip as a result of mechanicalgrinding, the protective film fills in the scratches, thereby reducingthe occurrence of cracks during the dicing step or in the finallypackaged device.

The process wherein the steps 1, 3 and 2 are conducted in this order isdescribed in detail below with reference to FIG. 3.

The 1-3-2 mode production process comprises the steps of:

applying the protective film forming layer 2 of the sheet 10 to form aprotective film for chips onto the back surface of the semiconductorwafer 3 having circuits on its surface (FIG. 3-A);

detaching the release sheet 1 from the protective film forming layer 2(FIG. 3-B);

dicing the semiconductor wafer 3 together with the protective film 2with respect to each circuit (FIG. 3C); and

curing the protective film forming layer 2 by heating or energy rayirradiation (FIG. 3-D) to obtain semiconductor chips having theprotective film 2 on its back surface (FIG. 3-E).

That is, the 1-3-2 mode production process is identical to the 1-2-3mode production process (FIG. 2), except that the protective filmforming layer 2 is cured after the dicing.

When the protective film forming layer 2 contains the thermosettingcomponent, the curing thereof is conducted by heating. Therefore, thedicing sheet is required to have sufficient heat resistance to avoidheat deterioration at the time of curing.

The process wherein the steps 2, 1 and 3 are conducted in this order isdescribed in detail with reference to FIG. 4.

The 2-1-3 mode production process comprises the steps of:

applying the protective film forming layer 2 of the sheet 10 to form aprotective film for chips onto the back surface of the semiconductorwafer 3 having circuits on its surface (FIG. 4-A);

curing the protective film forming layer 2 by heating or energy rayirradiation (FIG. 4-B);

detaching the release sheet 1 from the cured protective film forminglayer 2 (FIG. 4-C); and

dicing the semiconductor wafer 3 together with the protective film 2with respect to each circuit (FIG. 4-D) to obtain semiconductor chipshaving the protective film 2 on its back surface (FIG. 4-E).

That is, the 2-1-3 mode production process is identical to the 1-2-3mode production process, except that the release sheet 1 is detachedafter the protective film forming layer 2 is cured.

When the protective film forming layer 2 contains the thermosettingcomponent, the curing thereof is conducted by heating. Therefore, therelease sheet 1 is required to have sufficient heat resistance to avoidheat deterioration at the time of curing. Hence, films of, e.g.,polymethylpentene, polyethylene naphthalate and polyimide, are employedas the release sheet 1 because of their excellent heat resistance.

The process wherein the steps 2, 3 and 1 are conducted in this order isdescribed in detail with reference to FIG. 5.

The 2-3-1 mode production process comprises the steps of:

applying the protective film forming layer 2 of the sheet 10 to form aprotective film for chips onto the back surface of the semiconductorwafer 3 having circuits on its surface (FIG. 5-A);

curing the protective film forming layer 2 by heating or energy rayirradiation (FIG. 5B);

dicing the semiconductor wafer 3 together with the cured protective filmforming layer 2 with respect to each circuit (FIG. 5-C); and

detaching the release sheet 1 from the cured protective film forminglayer 2 (FIG. 5-D) to obtain semiconductor chips having the protectivefilm 2 on its back surface.

In this mode, the detaching of the release sheet 1 synchronizes with thepicking up of the chip. In other words, by picking up the chip, the chipis detached from the release sheet to give a semiconductor chip havingthe protective film on its back surface.

When the protective film forming layer 2 contains the thermosettingcomponent, the curing thereof is conducted by heating. Therefore, therelease sheet 1 is required to have sufficient heat resistance to avoidheat deterioration at the time of curing. Hence, films of, e.g.,polymethylpentene, polyethylene naphthalate and polyimide, are employedas the release sheet 1 because of their excellent heat resistance.

The process wherein the steps 3, 1 and 2 are conducted in this order isdescribed in detail with reference to FIG. 6.

The 3-1-2 mode production process comprises the steps of:

applying the protective film forming layer 2 of the sheet 10 to form aprotective film for chips onto the back surface of the semiconductorwafer 3 having circuits on its surface;

dicing the semiconductor wafer 3 together with the protective filmforming layer 2 with respect to each circuit;

detaching the release sheet 1 from the protective film forming layer 2;and

curing the protective film forming layer 2 by heating or energy rayirradiation to obtain semiconductor chips having the protective film onits back surface.

As shown in FIGS. 6-A to 6-C, this mode enables the dicing of the wafer3 fixed on the protective film forming layer 2. In this case, the sheet10 to form a protective film for chips has a function to act as aso-called dicing sheet. However, when the chip is mounted on a substratefor chips, the protective film forming layer has been already cured,losing the ability to act as a die bonding. Accordingly, the sheetemployed in the process for producing semiconductor chips of theinvention cannot be used as a dicing/die-bonding sheet.

The sheet 10 to form a protective film for chips fixing the wafer 3 onits protective film forming layer 2 can be fixed on a dicing sheet, asshown in FIGS. 6-D to 6-F, to go through the above procedures.

According to the present invention, a highly uniform protective film canbe readily formed on a back surface of a chip.

The process wherein the steps 3, 2 and 1 are conducted in this order isdescribed in detail with reference to FIG. 7.

The 3-2-1 mode production process comprises the steps of:

applying the protective film forming layer 2 of the sheet 10 to form aprotective film for chips onto the back surface of the semiconductorwafer 3 having circuits on its surface;

dicing the semiconductor wafer 3 together with the protective filmforming layer 2 with respect to each circuit;

curing the protective film forming layer 2 by heating or energy rayirradiation; and

detaching the release sheet 1 from the cured protective film forminglayer 2 to obtain semiconductor chips having the protective film on itsback surface.

That is, the 3-2-1 mode production process is identical to the 3-1-2mode production process (FIG. 6), except that the release sheet 1 isdetached from the protective film forming layer 2 after the protectivefilm forming layer 2 is cured.

As is mentioned earlier, the steps 1 to 3 can be performed in anarbitrary order without limitations in the first production process.Preferably, they are performed in the order of 1-2-3, 2-1-3, 3-1-2 or3-2-1.

FIGS. 2 to 7 illustrate the case where the curing for the protectivefilm forming layer is conducted by the use of a heating apparatus. Whenthe energy ray-curable component is used as the curable component, thecuring is performed using an energy ray irradiation equipment(ultraviolet ray irradiation equipment when ultraviolet ray being theenergy ray).

In the case where the second sheet to form a protective film for chipsis used, the protective film forming layer comprising both thethermosetting component and the energy ray-curable component as thecurable component is cured by heating and energy ray irradiation, whichcan be performed simultaneously or successively. Preferably, theprotective film forming layer formed on a back surface of the wafer isfirst half cured by energy ray irradiation and then completely byheating to make a protective film.

The second process for producing semiconductor chips having a protectivefilm on the back surface comprises:

adhering a protective film forming layer of the second sheet to form aprotective film for chips according to the present invention onto a backsurface of a semiconductor wafer having circuits on its surface,

curing the protective film forming layer by irradiation with energy ray,and thereafter, further conducting the following steps 1 to 3 in anarbitrary order:

Step 1: detaching the release sheet from the protective film forminglayer;

Step 2: further curing the protective film forming layer by heating;

Step 3: dicing the semiconductor wafer together with the protective filmforming layer with respect to each circuit.

The steps 1 to 3 can be performed in an arbitrary order withoutlimitations in the second production process likewise in the firstproduction process. Preferably, they are performed in the order of1-2-3, 2-1-3, 3-1-2 or 3-2-1.

When the protective film forming layer is cured by energy rayirradiation, the protective film forming layer loses tackiness and neversticks to other members even by the contact with other members under theusual storage conditions. Therefore, the series of the steps can besecurely carried out to thereby improve the workability.

According to the present invention, a highly uniform protective film canbe readily formed on a back surface of a chip, and, even if minutescratches are formed on the back surface of the chip as a result ofmechanical grinding, the chip is prevailed over adverse effectsresulting from the scratches.

EXAMPLES

The present invention is described in detail with reference to theexamples, which are not to limit the scopes of the invention in any way.The composition of the protective film forming layer, the wafer and theapparatuses used in the examples are shown below.

Protective Film Forming Layer 1

The protective film forming layer 1 was composed of a compositioncomprising:

15 parts by weight of a binder polymer composed of an acrylic polymer (acopolymer composed of 55 parts by weight of butyl acrylate, 15 parts byweight of methyl methacrylate, 20 parts by weight of glycidylmethacrylate and 5 parts by weight of 2-hydroxyethyl acrylate, andhaving a weight average molecular weight of 900,000 and a glasstransition temperature of −28° C.,

80 parts by weight of a thermosetting component composed of a mixedepoxy resin (30 parts by weight of a liquid epoxy-bisphenol A resin(epoxy equivalent: 180 TO 200), 40 parts by weight of a solidepoxy-bisphenol a resin (epoxy equivalent: 800 to 900) and 10 parts byweight of an epoxy-o-cresol novolak resin (epoxy equivalent: 210 to230),

0.6 part by weight of a heat-activatable latent epoxy resin curing agent(amine adduct type),

1.3 parts by weight of a black pigment (azo type), and a diluentsolvent.

Protective Film Forming Layer 2

The protective film forming layer 2 was composed of a compositioncomprising, in addition to the composition for the protective filmforming layer 1:

15 parts by weight of an energy ray (ultraviolet ray) curable component(trimethylolpropane triacrylate) and

4.5 parts by weight of a photopolymerization initiator(α-hydroxycyclohexylphenylketone).

Protective Film Forming Layer 3

The protective film forming layer 3 was composed of a compositioncomprising:

100 parts by weight of a binder polymer composed of an acrylic polymer(a copolymer composed of 65 parts by weight of butyl acrylate, 10 partsby weight of methyl methacrylate, 10 parts by weight of methyl acrylateand 15 parts by weight of 2-hydroxyethyl acrylate, and having a weightaverage molecular weight of 800,000 and a glass transition temperatureof −33° C.),

50 parts by weight of an energy ray (ultraviolet ray) curable component(trimethylolpropane triacrylate),

1.5 parts by weight of a photocurable component(α-hydroxycyclohexylphenylketone).

0.5 part by weight of a crosslinking agent (organic polyvalentisocyanato-based crosslinking agent (Coronate L, Nippon PolyurethaneIndustry Co., Ltd.)), and

a diluent solvent.

Wafer

An underground wafer having a diameter of six inches was ground to athickness of 200 μm using a grinding apparatus (Disco Co., DFG-840) at#2000 abrasion to prepare the wafer for the examples.

Sheet Applying Apparatus

Adwill RAD3500m/12 (Lintec Co., Ltd.)

Sheet Detaching Apparatus

Adwill RAD3000m/12 (Lintec Co., Ltd.)

Dicing Tape Mounter

Adwill RAD2500m/8 (Lintec Co., Ltd.)

Ultraviolet Ray Irradiation Apparatus

Adwill RAD2000m/8 (Lintec Co., Ltd.)

Dicing Apparatus

AWD4000B (Tokyo Seimitsu Co., Ltd.)

Forced Convection Constant Temperature Oven

DN610 (Yamato Scientific Co., Ltd.)

Dicing Sheet

Adwill G-11 (Lintec Co., Ltd.)

Example 1

A polyethyleneterephthalate film (Lintec Co., Ltd. SP-PET3811),thickness: 38 μm, surface tension: less than 30 mN/m) having beentreated for releasing at one surface was used as a release sheet. Thecomposition for the protective film forming layer 1 was coated on therelease-treated surface of the release sheet so as to have a thicknessof 30 μm after the solvent being removed by drying, thereby a sheet toform a protective film for chips was prepared. For protection of thecoated surface, a release-treated polyethyleneterephthalate film (LintecCo., Ltd. SP-PET3801) was laminated thereon.

The polyethyleneterephthalate film (SP-PET3801) was detached from thesheet to form a protective film for chips. The protective film forminglayer was applied onto the ground surface of the wafer using the sheetapplying apparatus. The peripheral edge of the sheet was removed alongthe wafer shape (FIG. 2A). The release sheet was detached using thesheet detaching apparatus (FIG. 2-B). The protective film forming layerwas cured by heating at 160° C. for 1 hour using the forced convectionconstant temperature oven (FIG. 2-C) to prepare a wafer having aprotective film.

A dicing sheet was applied on the protective film of the wafer using thedicing tape mounter. The wafer, together with the protective film, wasdiced into chips (10 mm×10 mm) by the use of the dicing apparatus toobtain objective chips having a protective film (FIGS. 2-D and 2-E).

Example 2

A polyethylenenaphthalate film (Teijin Ltd., Teonex), thickness: 25 μm,surface tension: less than 30 mN/m having been treated for releasing atone surface was used as a release sheet. The composition for theprotective film forming layer 1 was coated on the release-treatedsurface of the release sheet so as to have a thickness of 30 μm afterthe solvent being removed by drying, thereby a sheet to form aprotective film for chips was prepared. For protection of the coatedsurface, a release-treated polyethyleneterephthalate film (Lintec Co.,Ltd. SP-PET3801) was laminated thereon.

The polyethyleneterephthalate film was detached from the sheet to form aprotective film for chips. The sheet was applied on the ground surfaceof the wafer in the same manner as in Example 1. The peripheral edge ofthe sheet was removed along the wafer shape (FIG. 4-A).

The protective film forming layer was cured by heating at 160° C. for 1hour using the forced convection constant temperature oven (FIG. 4-B) toform a protective film on the ground surface of the wafer.

The release sheet was detached using the sheet detaching apparatus (FIG.4-C). A dicing sheet was applied on the protective film of the waferusing the dicing tape mounter. The wafer, together with the protectivefilm, was diced into chips (10 mm×10 mm) by the use of the dicingapparatus to obtain objective chips having a protective film (FIGS. 4-Dand 4-E).

Example 3

A polyethyleneterephthalate film (Lintec Co., Ltd. SP-PET3811 havingbeen treated for releasing at one side was used as a release sheet. Thecomposition for the protective film forming layer 3 was coated on therelease-treated surface of the release sheet so as to have a thicknessof 30 μm after the solvent has been removed by drying, thereby a sheetto form a protective film for chips was prepared. For protection of thecoated surface, a release-treated polyethyleneterephthalate film (LintecCo., Ltd. SP-PET3801) was laminated thereon.

The polyethyleneterephthalate film (SP-PET3801) was detached from thesheet to form a protective film for chips. The sheet was applied on theground surface of the wafer in the same manner as in Example 1. Theperipheral edge of the sheet was removed along the wafer shape (FIG.4-A).

The protective film forming layer was completely cured by ultravioletray irradiation dosed form the sheet side using the ultraviolet rayirradiation apparatus, thereby a wafer having a protective film wasobtained (not shown in the figure).

The release sheet was detached using the sheet detaching apparatus (FIG.4-C). A dicing sheet was applied onto the protective film of the waferusing the dicing tape mounter. The wafer, together with the protectivefilm, was diced into chips (10 mm×10 mm) using the dicing apparatus toobtain objective chips having a protective film (FIGS. 4-D and 4-E).

Example 4

The composition for the protective film forming layer 2 was coated onthe release-treated surface of a polyethyleneterephthalate film (LintecCo., Ltd. SP-PET3801) having been treated for releasing at one surfaceso as to have a thickness of 50 μm after the solvent being removed bydrying. As a release sheet, a linear low-density polyethylene film(thickness: 110 μm, surface tension: 32 mN/m) was applied onto thecoated surface, thereby a sheet to form a protective film for chips wasprepared.

The protective film forming layer of the sheet to form a protective filmfor chips was applied on the ground surface of the wafer using thedicing tape mounter, and a laminate thus formed was fixed by a ringframe (FIG. 6-A).

The protective film forming layer was half cured by ultraviolet rayirradiation dosed from the sheet side using the ultraviolet rayirradiation apparatus A(not shown in the figure).

The wafer, together with the protective film, was diced into chips (10mm×10 mm) using the dicing apparatus to obtain objective chips having aprotective film forming layer (FIGS. 6-B and 6-C).

The respective chips were heated at 160° C. for 1 hour suing the forcedconvection constant temperature oven (FIG. 6-G) to cure the protectivefilm forming layer, thereby objective chips having a protective filmwere obtained.

Example 5

The composition for the protective film forming layer 2 was coated onthe release-treated surface of a polyethyleneterephthalate film (LintecCo., Ltd. SP-PET3801) having been treated for releasing at one surfaceso as to have a thickness of 30 μm after the solvent being removed bydrying. As a release sheet, a linear low-density polyethylene film(thickness: 110 μm, surface tension: 32 mN/m) was applied onto thecoated surface, thereby a sheet to form a protective film for chips wasprepared.

The polyethyleneterephthalate film was detached from the sheet to form aprotective film for chips. The protective film forming layer was appliedon the ground surface of the wafer in the same manner as in Example 1,and the peripheral edge of the sheet was removed along the wafer shape(FIG. 2-A).

The protective film forming layer was half cured by ultraviolet rayirradiation dosed from the sheet side using the ultraviolet rayirradiation apparatus to eliminate its tackiness (not shown in thefigure).

After the release sheet was detached using the sheet detaching apparatus(FIG. 2-B), the protective film forming layer was completely cured byheating at 160° C. for 1 hour using the forced convection constanttemperature oven (FIG. 2-C) to prepare a wafer having a protective film.

The wafer, together with the protective film, was diced into chips (10mm×10 m in the same manner as in Example 1 to obtain objective chipshaving a protective film (FIGS. 2-D and 2-E).

1. A sheet to form a protective film for chips comprising a release sheet and a protective film forming layer formed on a detachable surface of the release sheet, wherein said protective film forming layer comprises an energy ray-curable component and a binder polymer component.
 2. The sheet to form a protective film for chips according to claim 1, wherein the binder polymer component is composed of an acrylic polymer.
 3. The sheet to form a protective film for chips according to claim 1, wherein the energy ray-curable component is composed of an ultraviolet ray-curable resin.
 4. A sheet to form a protective film for chips comprising a release sheet and a protective film forming layer formed on a detachable surface of the release sheet, wherein said protective film forming layer comprises a thermosetting component, an energy ray-curable component and a binder polymer component.
 5. The sheet to form a protective film for chips according to claim 4, wherein the binder polymer component is composed of an acrylic polymer.
 6. The sheet to form a protective film for chips according to claim 4, wherein the energy ray-curable component is composed of an ultraviolet ray-curable resin. 